The proposed research is based on the proposition that specializations have evolved in both the design of primate vocalizations and in the structure of auditory and perceptual systems that act to promote acoustic communication under the adverse conditions found in nature. Under natural conditions communicative signals are embedded in background noises, and are subjected to degradation by wind and thermal drafts, and by the processes of absorption, diffraction and reflection. Thus vocal communication is critially constrained by the acoustics of the habitat. The proposed research explores the interface between the perceptual mechanisms of primates and their acoustic ecology. The specific goal of this research is to characterize the acoustic ecology of two species of forest primates, and to psychophysically measure the detection, discrimination and localization of species-specific vocalizations, and the attendant impairment of these processes by ecological factors. A final objective of this work is to perceptually and acoustically isolate the communicatively relevant elements of primate vocal signals. These elements may subsequently be shown to have phoneme-like qualities. The ecological perspective advanced here complements the speech-centered approach of my colleagues. It is hoped that the interplay between these two approaches will reveal the organization of primate communication systems, and ultimately the origin of speech.